Iii-v laser platforms on silicon with through silicon vias by wafer scale bonding

ABSTRACT

A laser integrated photonic platform to allow for independent fabrication and development of laser systems in silicon photonics. The photonic platform includes a silicon substrate with an upper surface, one or more through silicon vias (TSVs) defined through the silicon substrate, and passive alignment features in the substrate. The photonic platform includes a silicon substrate wafer with through silicon vias (TSVs) defined through the silicon substrate, and passive alignment features in the substrate for mating the photonic platform to a photonics integrated circuit. The photonic platform also includes a III-V semiconductor material structure wafer, where the III-V wafer is bonded to the upper surface of the silicon substrate and includes at least one active layer forming a light source for the photonic platform.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of co-pending U.S. patent applicationSer. No. 16/234,105 filed Dec. 27, 2018. The aforementioned relatedpatent application is herein incorporated by reference in its entirety.

TECHNICAL FIELD

Embodiments presented in this disclosure generally relate to lasersincluding III-V semiconductor material and the fabrication thereof.

BACKGROUND

The cost of production and the physical properties of lasers areinfluenced by the materials and methods used in producing those lasers.The choices made in the production methods and construction materialsnot only affect the yield for a given batch of lasers, but also affectthe size of the batches. As a result, lasers are often produced onspecialized equipment and in smaller batches than other electrical oroptical components. Additionally, due to material differences in thelaser from the other components, special techniques and materials areoften used to integrate the lasers with other electrical or opticalcomponents to create a final assembly, which the other components do notrequire to integrate with one another, further adding to the costs ofproduction.

BRIEF DESCRIPTION OF THE DRAWINGS

So that the manner in which the above-recited features of the presentdisclosure can be understood in detail, a more particular description ofthe disclosure, briefly summarized above, may be had by reference toembodiments, some of which are illustrated in the appended drawings. Itis to be noted, however, that the appended drawings illustrate typicalembodiments and are therefore not to be considered limiting; otherequally effective embodiments are contemplated.

FIG. 1 illustrates a frontal cut-away view of a laser platform accordingto embodiments described herein.

FIGS. 2A-K illustrate various views of the fabrication of a laserplatform according to embodiments described herein.

FIGS. 3A-C illustrate various views of the fabrication of a laserplatform at a wafer level according to embodiments described herein.

FIG. 4 is a flow chart outlining general operations in an example methodto produce the a laser platform according to embodiments describedherein.

To facilitate understanding, identical reference numerals have beenused, where possible, to designate identical elements that are common tothe figures. It is contemplated that elements disclosed in oneembodiment may be beneficially used in other embodiments withoutspecific recitation.

DESCRIPTION OF EXAMPLE EMBODIMENTS Overview

One embodiment presented in this disclosure includes a wafer thatincludes a silicon substrate with an upper surface and one or morethrough silicon vias (tsvs) defined through the silicon substrate. Thewafer also includes a III-V semiconductor material structure bonded tothe upper surface of the silicon substrate including at least one activelayer independently grown on the structure prior to bonding, where theat least one active layer forms a laser.

Another embodiment presented in this disclosure includes a photonicplatform that includes a silicon substrate including an upper surface,one or more through silicon vias (tsys) defined through the siliconsubstrate, and passive alignment features in the substrate. The photonicplatform also includes a III-V semiconductor material structure bondedto the upper surface of the silicon substrate including at least oneactive layer independently grown on the structure prior to bonding,where the at least one active layer forms the laser for the photonicplatform.

Another embodiment presented in this disclosure includes a method thatincludes independently forming a silicon substrate including a bondinglayer on an upper surface; independently forming a III-V semiconductormaterial structure including a grown active layer; bonding the III-Vsemiconductor material structure to the bonding layer on the uppersurface of the substrate to create bonded structure; and forming aphotonic platform in the bonded structure.

EXAMPLE EMBODIMENTS

As described above, in the production and fabrication of siliconphotonic integrated circuits (PICs), the various fabrication processeshave been abstracted out so that various components can evolve anddevelop separately and so that various manufacturing/fabricationprocesses can be implemented at different phases of the manufacturingprocess without interfering with process of the other phases. Forexample, in some methods the production and development of electronicintegrated circuits (EICs) has been decoupled from the production anddevelopment of PICs. This allows the PIC and EIC of various silicon PICsto evolve separately to ease development and manufacturingcomplications. The separation of the fabrication processes also allowsfor a faster time to market as technologies in each of the PIC and EICimprove.

There are also additional developments that further component decouplingcan improve. For example, the laser of the silicon photonic IC, which isa critical component of the PIC, can be decoupled and developedseparately from the modulation, detection, and multiplexing functions ofthe PIC. However, it is often important to maintain a preciseintegration of the laser and PIC, and for the PIC to maintain a preciseintegration to the EIC. Previous III-V laser fabrication processes werecompleted entirely on native III-V substrates which must then be bondedto partially processed silicon-on-insulator (SOI) chips including theheterogeneous III-V substrate platforms.

The methods and photonics/laser platform described herein enableindependent fabrication of a laser platform with a low thermal impedancewhile also providing for precise laser and PIC integration. In someexamples, portions of the laser platform, including a substrate, areindependently made of silicon (Si) apart from an epitaxial growthprocess of III-V material, such that the growth processes does not addany additional stress to bonding interfaces between the III-V materialand a silicon substrate and to leverage features such as through siliconvias (TSVs) in the substrate of the laser platform and low thermalimpedance bonds. Furthermore, economies of scale can be leveraged byfabricating the laser platforms at a Si wafer scale.

A completed laser platform describe herein can provide butt coupling ofthe independently developed laser platform and the independently developPIC by directly attaching a laser platform holding the laser to the PICin a carefully aligned manner using mechanical alignment featuresdescribed herein. For example, an end facet of a laser platform may becoupled with an end facet of a PIC to provide a broadband solution thatis designed with low back reflection. An example laser platform isdiscussed in relation to FIG. 1 and the fabrication of the laserplatform is discussed in relation to FIGS. 2A-2K.

FIG. 1 illustrates a frontal cut-away view of a laser platform 100according to embodiments described herein. The laser integrated photonicplatform, laser platform 100, includes a substrate 108. In someexamples, the substrate is a Si substrate fabricated separately and/orindependently from one or more other components of the laser platform100. As shown, the substrate 108 includes one or more TSVs 110 definedthrough the substrate 108. In some examples, the TSVs 110 are formed inthe substrate 108 prior to the substrate being bonded/coupled to othercomponents in the substrate. In some examples, the TSVs 110 are formedin the substrate 108 subsequent to the substrate being bonded/coupled toother components in the substrate, as described herein. In someexamples, the TSVs 110 include gold (Au) and/or copper (Cu) TSVs. Insome examples, the substrate 108 includes an upper surface 109, whichfunctions as an end facet for a coupling between the substrate 108 andother components of the laser platform, such as a III-V semiconductormaterial structure 102 described next.

As shown, the III-V semiconductor material structure 102 is bonded tothe substrate 108 and the upper surface 109. In some examples, thestructure 102 is independently formed/grown separately from othercomponents of the laser platform 100, such as the substrate 108. Thisincludes the formation/growth of an active layer 106 in the structure102. The active layer 106 includes one or more layers to form a laser.In one example, the active layer 106 includes active layers formingquantum wells (QW) making the laser platform 100 a QW laser. In anotherexample, the active layer 106 includes active layers forming quantumdots (QD), making the laser platform 100 a QD laser. Quantum Wells aretwo-dimensional structures formed by a thin layer of a first materialsurrounded by wider-bandgap material and that allow electronic capturein one dimension (allowing planar two-dimensional movement). QuantumDots can act as zero-dimensional entities, which enablesthree-dimensional capture of excited electrons (not allowing movement).When sufficient voltage is applied across the active layer 106, acurrent flows through the active layer 106 and emits a laser from thelaser platform 100 forming a light source.

As also shown in FIG. 1, the laser platform 100 includes apassivation/isolation boundary 105 which provides a protection andinsulation barrier between the structure 102 and a top metal layer 104and other environmental factors that may lead to degradation of thestructure 102 and active layer 106. The laser platform 100 also includesa bottom metal layer 112. In some examples, the metal layers 104 and 112are applied through metallization as described in more detail inrelation to FIG. 2H-I. In some examples, the metallization step formsthe TSVs 110 after the structure 102 is bonded to the substrate 108. Themetal layers 104 and 112 may also include electrical leads for the laserplatform 100, where the electrical leads are positioned such that othercomponents can be physically attached to and/or electrically connectedto the laser platform 100. The other components such as other PICcomponents and/or other EIC components may also beconnected/coupled/joined to the laser platform 100 using the mechanicalfeatures 114.

In some examples, the mechanical features 114 include lithographicalignment features that can be mated and/or interlocked with one or moresilicon photonic components, providing a sub-micron level passivealignment feature. For example, the alignment features may be used toalign and mate optical waveguides in the laser platform 100 to otherwaveguides such as an input waveguide in a PIC, during coupling of thelaser platform 100 to the PIC. In this example, the waveguides typicallyrequire a highly precise alignment (e.g., alignment within 1 micron). Insome examples, the mechanical features including passive alignmentfeatures such as v-grooves, u-grooves, etc. In some examples, themechanical features 114 are formed in the substrate after the structure102 and the substrate 108 are bonded.

As shown, the laser platform 100 include components that are able to befabricated independently of the PIC and the EIC, such that the laserplatform can be developed independent of the other components of siliconphotonics chip. Various methods to fabricate the laser platform will nowbe discussed in relation to FIGS. 2A-K and FIGS. 3A-B.

FIGS. 2A-K illustrate various views of the fabrication of a laserplatform, such as laser platform 100, according to embodiments describedherein. FIG. 2A-B illustrates a first independent state of fabricationwhere a substrate 108 is formed. In some examples, the substrate 108 isa bulk substrate of a first wafer, wafer 302 shown in FIG. 3A. As shownin FIG. 3A, the wafer 302 includes TSVs 310. In some examples, the wafer302 may comprise a 200 mm×300 mm wafer. In some examples, the substrate108 (and the wafer 302) is a Si substrate. As shown in FIG. 2A, thesubstrate 108 includes an upper surface 201. In some examples, as shownin FIG. 2B, the substrate goes through a front end (prior to bonding)metallization process to form one or more TSVs 110 in the substrate 108.

In some examples, a bonding layer 203 is a formed on the upper surface201 to enable a planar bonding surface. In some examples, the bondinglayer 203 includes a deposited metallic bonding surface deposited on thesubstrate 108 and the upper surface 201. In some examples, the depositedmetallic bonding surface enables a conductive bonding between thesubstrate 108 and the III-V semiconductor material structure 102. Insome examples, the bonding layer 203 is a degenerately doped bondingsurface, including silicon and/or silicon dioxide. In some examples, thedegenerately doped bonding surface provides a conductive bonding betweenthe silicon substrate 108 and the III-V semiconductor material structure102. In another example, the bonding layer 203 is a doped surface on thesubstrate. For example, the upper surface 201 may be doped such as thatthe doped upper surface 201 forms the bonding layer 203. In everyembodiment, the bonding layer 203 allows for the substrate 108 to becoupled/bonded to an independently fabricated III-V semiconductormaterial structure 102, as described in relation to FIGS. 2C-D.

FIGS. 2C-D also shows an independent first state of fabrication for thelaser platform 100. As described above, the III-V semiconductor materialis fabricated/grown independently from the substrate 108, where a firstportion 201 a of the III-V semiconductor material structure 102 isformed/provided, as shown in FIG. 2C. In some examples, the firstportion 201 a is formed using epitaxial growth of a III-V semiconductormaterial and includes a low defect density and a Root Mean Square (RMS)roughness of approximately one nanometer or less. Once the first portion201 a is formed, the forming of the active layer 106 begins with theepitaxial growth of the quantum confined structures 206, as shown inFIG. 2D. In some examples, the structures 206 include QWs to form a QWlaser. In another example, the structures 206 include QDs to form a QDlaser. In some examples, the III-V semiconductor material structure 102is a bulk substrate of a second wafer, wafer 304 shown in FIG. 3A. Asshown in FIG. 3A, the wafer 304 includes the quantum confined structures206. In some examples, the III-V material structure 102 may also beprocessed to incorporate one or more waveguides into the structure 102.

As also shown in FIG. 2D, a second portion 201 b of the III-Vsemiconductor material structure 102 is provided in order to completethe structure 102. The structure 102 includes an upper surface 202. Insome examples, a bonding layer 204 is a formed on the upper surface 202.In some examples, the bonding layer 204 includes a doped bondingsurface, where the bonding surface is doped prior to the bonding andassists/provides an ohmic contact post bonding. In some examples, thedoped bonding layer 203, shown in FIG. 2B, and the doped bonding layer204 provide a conductive bonding between the silicon substrate 108 andthe III-V semiconductor material structure 102. In another example, themetallic and/or degenerately doped bonding layer 203 provides theconductive bonding between the substrate 108 and the structure 102. Insome examples, the bond between the substrate 108 and the structure 102is classified as a low thermal impedance bond.

Low thermal impedance bonds in the laser platform 100 and a low thermalimpedance substrate allow the active temperature of the laser to be muchlower than alternative high impedance laser platforms. In some examples,lower temperatures in the functioning of the laser result in a higheroptical power/output and a longer lifetime of the laser platform. Insome embodiments, when a large area of the substrate 108 is used tointerface the entire structure of the laser platform 100 and/or the PICwith a heat sink, the thermal path from the active layers of the laserand that heat sink may be approximately 10 Kelvins/Watt per mm. Afterthe bonding layer 203 and the bonding layer 204 are formed on thesubstrate 108 and the structure 102 respectively, the components areready for bonding as shown in FIG. 2E.

FIG. 2E illustrates the upper surface 202 bonded to the upper surface201 forming the intermediate structure 210. In some examples, thebonding process may include anodic bonding, O2 plasma activated bonding,and/or other Van der Waal bonds in either an ambient environment or avacuum environment. FIG. 3B is an example of the upper surface 202bonded to the upper surface 201 at a wafer level, that is the bonding ofthe second wafer 304 to the first wafer 302, forming the intermediate(pre-processed) wafer 350 used as a base for the laser platformsdescribed herein. The upper surface 202 may be bonded to the uppersurface 201 using a low temperature bonding processes including a plasmaassisted bonding, oxide free van der Waals bonding (e.g., with pressureunder vacuum to remove native oxide), adhesive bonding, etc.

Once the intermediate structure 210 is bonded together, a form 211 isdefined in the structure 210 as shown in FIG. 2F. In some examples, theform 211 is a form for the structure 102 in the completed laser platform100, as shown in FIG. 1. In FIG. 2G, the form 211 is used to etch thestructure 102 such that it takes the shape of the structure 216. Theetching of the structure 102 can include a chemical and/or mechanicaletching process.

Once the structure 102 is etched into the structure 216, the structure216 is covered with the passivation/isolation boundary 105 to protectthe structure 102 and to provide isolation/insulation between thestructure 102 and the other components of the laser platform 100. Forexample, the passivation/isolation boundary 105 may include a dielectriclayer such as Silicon Nitride or Silicon dioxide layer, where theboundary 105 is evaporated onto the surface of the structure 102 andpatterned to open a P-ridge. In FIG. 2I, the metal layer 220 is added ina metallization process. In FIG. 2J, the mechanical features 114 areformed in the substrate 108 though lithographic and/or mechanicalgrinding/etching. In some examples, the mechanical features 114 areformed in relation to the bonded structure 102, such that when the laserplatform 100 is bonded with a PIC, the laser can be precisely alignedwith the PIC components.

Furthermore, in some examples the structure 216 is defined in thesubstrate 108 and the substrate is thinned by removing the structure 216from the substrate FIG. 3C is an example of a processed wafer 360 wherea bonded structure such as the processed wafer 360 includes theindividual dies of formed laser platforms 362 (e.g., laser platform100), prior to dicing of the wafer. Additional metallization processescomplete backside metal layers 112 to form the laser platform 100 asshown in FIG. 2K. In some examples, additional photonic elements such aswaveguides etc., may also be added to the formed laser platform 100. Insome examples, the completed laser platform can be tested at a waferlevel to determine function and quality of individual laser platforms inthe wafer. Example tests include, but are not limited to: deviceburn-in, wavelength characterization, light-current-voltagecharacterization, threshold measurements, wafer maps, photoluminescence,process monitoring, physical dimensions, etc. Once a wafer is diced, thefunctioning lasers may then be coupled to a PIC. While the fabricationsteps are described in detailed terms in relation to FIGS. 2A-2K, thefabrication of the laser platform 100 may also be described in moregeneral terms such as described in relation to FIG. 4.

FIG. 4 is a flow chart outlining general operations in an example methodto produce the a laser platform according to embodiments describedherein. Reference will be made to previous Figs. as described above.Method 400 begins with operation 402, where a silicon substratecomprising a bonding layer on an upper surface is independently formed,such as described in relation to FIGS. 2A and 2B. In some examples, thesilicon substrate includes one or more TSVs formed in the substrate, asshown in FIG. 2B. In some examples, the bonding layer is formed suchthat it provides a conductive bonding between the silicon substrate andthe III-V semiconductor material structure.

Method 400 proceeds to operation 404, where a III-V semiconductormaterial structure including a grown active layer is independentlyformed, such as is described in relation to FIGS. 2C and 2D. In someexamples, the independent formation of the III-V semiconductor materialstructure requires high heat and other processing conditions that woulddamage components of the silicon substrate formed in operation 402. Theindependent formation of the substrate and the structure allows forproperties, such as the TSVs to be formed and/or deposited on thesubstrate without damage from the III-V growth processes.

At operation 406, the III-V semiconductor material structure is bondedto the bonding layer on the upper surface of the substrate to create abonded structure, as described above in relation FIG. 2E.

At operation 408, a laser platform is formed in the bonded structure,such as described in relation to FIGS. 2F-K. The formation processinclude at least removing excess III-V semiconductor material structureusing an etching process to form the structure 216 described in FIGS. 2Fand 2G. Additionally, passivation and/or isolation processes can beapplied to the structure 216 to apply the boundary 105 as described inrelation to FIG. 2H. In some examples, additionally TSVs may be formedin the substrate 108 described in relation the FIG. 2I usingmetallization processes that also deposit metal layers 104 and 112described in relation to FIGS. 2I and 2K. Additionally, a plurality ofmechanical features 114, as well as photonic elements such as waveguidesetc., may be formed in the substrate of the bonded structure, such asthe structure 260 as described in relation to FIG. 2J.

In the current disclosure, reference is made to various embodiments.However, the scope of the present disclosure is not limited to specificdescribed embodiments. Instead, any combination of the describedfeatures and elements, whether related to different embodiments or not,is contemplated to implement and practice contemplated embodiments.Additionally, when elements of the embodiments are described in the formof “at least one of A and B,” it will be understood that embodimentsincluding element A exclusively, including element B exclusively, andincluding element A and B are each contemplated. Furthermore, althoughsome embodiments disclosed herein may achieve advantages over otherpossible solutions or over the prior art, whether or not a particularadvantage is achieved by a given embodiment is not limiting of the scopeof the present disclosure. Thus, the aspects, features, embodiments andadvantages disclosed herein are merely illustrative and are notconsidered elements or limitations of the appended claims except whereexplicitly recited in a claim(s). Likewise, reference to “the invention”shall not be construed as a generalization of any inventive subjectmatter disclosed herein and shall not be considered to be an element orlimitation of the appended claims except where explicitly recited in aclaim(s).

In view of the foregoing, the scope of the present disclosure isdetermined by the claims that follow.

We claim:
 1. A method, comprising: forming a silicon substratecomprising a bonding layer; forming a III-V semiconductor materialstructure comprising a grown active layer; bonding the III-Vsemiconductor material structure to the bonding layer of the siliconsubstrate to create a bonded structure; and forming a laser integratedphotonic platform in the bonded structure.
 2. The method of claim 1,wherein forming the laser integrated photonic platform in the bondedstructure comprises: removing excess III-V semiconductor materialstructure using an etching process; and forming a plurality ofmechanical alignment features in the silicon substrate of the bondedstructure.
 3. The method of claim 1, further comprising: forming one ormore through silicon vias (TSVs) in the silicon substrate, wherein theone or more TSVs are formed in the silicon substrate prior to bondingthe III-V semiconductor material structure to the bonding layer of thesilicon substrate.
 4. The method of claim 1, wherein the method furthercomprises: forming the bonding layer on the silicon substrate, whereinthe bonding layer provides a conductive bonding between the siliconsubstrate and the III-V semiconductor material structure.
 5. The methodof claim 4, wherein the bonding layer comprises a deposited metallicbonding surface enabling conductive bonding between the siliconsubstrate and the III-V semiconductor material structure.
 6. The methodof claim 1, wherein the grown active layer comprises a plurality ofquantum wells.
 7. The method of claim 1, wherein the grown active layercomprises a plurality of quantum dots.
 8. The method claim 1, whereinthe bonding layer comprises a doped surface, wherein the III-Vsemiconductor material structure further comprises a degenerately dopedbonding surface, wherein the degenerately doped bonding surface providesa conductive bonding between the silicon substrate and the III-Vsemiconductor material structure.
 9. The method of claim 1, wherein thebonding layer comprises a doped upper surface and the III-Vsemiconductor material structure further comprises a doped bondingsurface, wherein the doped upper surface and the doped bonding surfaceprovide a conductive bonding between the silicon substrate and the III-Vsemiconductor material structure.
 10. The method of claim 1, wherein abond between the III-V semiconductor material structure and the bondinglayer of the silicon substrate is a low thermal impedance bond.
 11. Themethod of claim 1, wherein the silicon substrate further comprises oneor more TSVs, formed after the III-V semiconductor material structure isbonded to the bonding layer of the silicon substrate, one or moremechanical features defined in the silicon substrate, and one or morephotonic elements.
 12. The method of claim 1, wherein the bondedstructure comprises a plurality of individual laser dies.